How Stuff Works

Different ways to create motion sensors:

LIGHT SENSORS
A beam of light crosses a space, and is detected by a photo sensor which rings a bell if the light source is interrupted.

RADAR
http://www.howstuffworks.com/radar.htm
Echo and Doppler Shift



An echo is created by sound bouncing off a surface and returning in the direction it came. The time of the return of the echo is determined by the distance of the surface creating the echo.




Doppler shift is the difference in tone of a sound as it approaches and when it is past you. Eg a car or even a plane.
You can combine echo and Doppler shift in the the same manner as the echo bouncing off an approaching object, to create motion sensors. The echo of a sound can determine how far away something is, and Doppler shift iof the echo determines how fast something is going.



Ultrasound
Ultrasound is used instead of sound radar so as not to disrupt everyday use of
Things like police radar, satalite mapping etc. (often used in medical procedures as
Well) Sonar is “sound radar” but sound does not travel very far, and everyone can hear
Sounds, submarines use sound radar or sonar.
Radar uses radio waves instead of sound. Radio waves travel a long way arn are invisible to
Humans and easy to detect even when faint.
Radio waves transmit data invisibly, through the use of wireless technologies, using
Radio waves to communicate.
http://computer.howstuffworks.com/question238.htm


About radio controlled toys:
Basic principles
Transmitter sends radio waves to the receiver (sends signal over a frequency, using
A powersource such as a 9volt battery for the power and transmission). Basic
Consumer items use 27MHz or 49MHz, eg RC toys, garage doors openers etc. More
Sophisticate RC model planes use 72 or 75 MHz. The idea with this is that two can
Be operated at the same time without interference between two transmitters.
Receiver relies on an antenna and circuit board receives signals from transmitter and activates motors
Motors can cause wheels to turn lights to flash etc.
Power source eg batteries.
http://www.howstuffworks.com/rc-toy.htm
Remote control toys etc have a wire connecting the controller and the toy.
Radio contol is always wireless.



Note on Radio Frequencies:
A radio wve is an electromagnetic wave propagated by an antenna.Radio waves have
Different frequencies, and by turning a receiver to a specific frequency you can pick up specific signals
http://electronics